This invention relates to piston ring assemblies for pistons of internal combustion engines, more particularly to piston ring assemblies each having a pair of rails engageable with a cylinder wall and a spacer and expander member for holding the rails in axially spaced relation and for expanding the rails radially outwardly.
Pistons of internal combustion engines are equipped with several types of piston rings to prevent leakage of combustion gas and consumption of oil. One of the piston rings comprises a pair of rails engageable with a cylinder wall and a spacer and expander member for holding and expanding the rails.
The typical piston ring assembly is disclosed in U.S. Pat. No. 2,831,738 in which FIGS. 23 to 27 show the piston ring assembly having arms extending alternately upwardly and downwardly from lower and upper crowns of the corrugated spacer and expander member thereof. The rails supported on the crowns are urged radially outwardly due to self-expansion force of the spacer and expander member and engage the cylinder wall under springable compression when mounted in a groove of the piston and compressed. The arms abutting the inner peripheries of the rails assist in offering the rails the resilient spring-like action to exert the outward radial load thereon. It is noted that the conventional arms extend vertically only. However, it has been found that arms so formed do not provide the proper outward radial load on the rails to obtain high overall conformability of the rails to the cylinder wall.